In general, broadcast instruments such as a video camera execute an edge compensation process for improving the definition of an image thereof. FIG. 1 shows a representative edge compensation circuit for processing an image signal. Red, green and blue (R, G and B) image signals are generated by a photoelectric converting element such as a charge-coupled device (CCD). Then, an edge compensation operation is respectively executed for the R, G and B image signals by the edge compensation circuit as shown in FIG. 1. In FIG. 1, a red edge compensator 20, a green edge compensator 10 and a blue compensator 40 are divided into horizontal and vertical edge compensator, respectively. The red and blue edge compensators 20 and 40 perform the edge compensation operation according to a vertical edge compensating signal output from the green edge compensator 10. In the edge compensating operation, a first 1H delayer 11 delays the G image signal input through a second input terminal P2 by 1H to output the delayed G image signal to a second 1H delayer 12. The second 1H delayer 12 further delays the G image signal by 1H to output a 2H-delayed G image signal. A second adder 13 adds the G image signal input from the second input terminal P2 to the 2H-delayed G image signal output from the second 1H delayer 12 to thereby output the added signal to a second amplifier 14. The second amplifier 14 amplifies the added signal output from the second adder 13 by a factor of 0.5. A third adder 15 adds the 1H-delayed G image signal from the first 1H delayer 11 to the amplified signal from the second amplifier 14 to thereby output the added signal as a vertical edge compensating signal. Further, a second delayer 31 delays the 1H delayed G image signal output from the first 1H delayer 11 during time period of t, and then outputs the delayed G image signal to a fourth amplifier 32. The fourth amplifier 32 amplifies the delayed G image signal by a factor of 2 and outputs the amplified signal to a fourth adder 34. Moreover, a second low pass filter LPF 33 filters the 1H-delayed G image signal output from the first 1H delayer 11, and outputs the filtered signal to the fourth adder 34. Here, the fourth adder 34 adds the added signal output from the third adder 15 to the amplified signal from the fourth amplifier 32 and to the G image signal low-pass-filtered by the second LPF 33, and outputs an edge-compensated G image signal to a fifth amplifier 52. The fifth amplifier 52 amplifies the edge-compensated G image signal from the fifth adder 52 by a factor of 0.59 and outputs the amplified signal to a sixth adder 54.
In the meanwhile, a first delayer 21 delays the R image signal input from a first input terminal P1 during the time period t, and outputs the delayed R image signal to a first amplifier 22. The first amplifier 22 amplifies the delayed R image signal by a factor of 2 and outputs the amplified signal to a first adder 24. Moreover, a first low pass filter LPF 23 filters the R image signal input from the first input terminal P1 to output the filtered signal to the first adder 24. Here, the first adder 24 adds the vertical edge-compensated G image signal output from the third adder 15 to the amplified R image signal output from the first amplifier 22 and to the R image signal low-pass-filtered by the first LPF 23, and outputs an edge-compensated R image signal to a second amplifier 51. The second amplifier 51 amplifies the edge-compensated R image signal from the first adder 24 by a factor of 0.3 and outputs the amplified signal to the sixth adder 54.
Further, a third delayer 41 delays the B image signal input from a third input terminal P3 during the time period t, and outputs the delayed B image signal to a sixth amplifier 42. The sixth amplifier 42 amplifies the delayed B image signal by a factor of 2, and outputs the amplified signal to a fifth adder 44. Moreover, a third low pass filter LPF 43 filters the B image signal received from the third input terminal P3, and outputs the filtered signal to the fifth adder 44. Here, the fifth adder 44 adds the vertical edge-compensated G image signal from the third adder 15 to the amplified B image signal from the sixth amplifier 42 and to the B image signal low-pass-filtered by the third LPF 43, and outputs an edge-compensated B image signal to a seventh amplifier 53. The seventh amplifier 53 amplifies the edge-compensated B image signal output from the fifth adder 44 by a factor of 0.11, and outputs the amplified signal to the sixth adder 54. The sixth adder adds the 0.3 R image signal amplified from the second amplifier 51 and the 0.59 G image signal amplified from the fifth amplifier 52 to the 0.11 B image signal amplified from the seventh amplifier 53, and outputs the added signal as a luminance signal Y.
The conventional edge compensation circuit, as discussed above, has a disadvantage in that a desired edge compensation value can not be obtained when the temperature changes the delay of the signal through the filters and adders, causing the edge compensation operation to be executed in a distorted state. In addition, the volume of the system becomes larger and the cost of production thereof becomes higher, because the PCB space is occupied by a plurality of manual elements included therein. Further, whenever the functional characteristics thereof are intended to be changed by embodying the above algorithm in a digital ASIC chip, there is a problem in that the ASIC design work must be repeated.